Fibers for nonwoven or textile materials must have certain characteristics in order to be considered useful or desirable. Important performance characteristics to consider in selecting a fiber or fibers for a wide range of nonwoven, knitted and woven products include the following: (1) fiber processability on nonwoven and textile equipment (efficiency, cost effectiveness); (2) fiber/fabric/material "hand" and overall aesthetics when viewed, touched, used or worn (abrasiveness, softness, fiber-covering power, opacity, comfort, drape, appearance, perception of suitability); (3) strength; (4) abrasion resistance; and (5) when applicable, liquid-transport characteristics (wetting, wicking, absorption, liquid-transport durability).
Nonwoven materials are manufactured by means other than weaving and knitting. The terms "nonwoven" and "nonwoven fabric" are general descriptive terms for a broad range of products, such as absorbent pads, wiping/cleaning webs or fabrics, insulation, aroma/flavor materials, liners, wicks, relatively thick battings, compressed bonded battings or webs, bandages, incontinence structures, filters and many other products. Interest in nonwoven materials is enhanced by the fact that such materials can be mass produced efficiently and at relatively low cost to satisfy many important consumer and industrial needs. Improvements in man-made fibers have contributed to the development of the nonwoven industry.
Man-made materials have become increasingly plentiful and inexpensive. However, in certain characteristics many of these materials do not compare well to natural fibers such as in the ability to transport moisture satisfactorily. Several methods have been devised to improve the characteristics of man-made natural fiber, such as cotton. U.S. Pat. Nos. 2,590,402, 2,781,242, 2,828,528 and 4,008,044 and the Journal of Applied Polymer Science, Vol. 33, Page 455 (1987) all disclose the treatment of certain polyester fabrics with caustic to improve certain properties such as handle and softness. U.S. Pat. No. 4,374,960 discloses the production of polyester fibers of improved stability that are made by mixing the polyester and an end-capping reagent prior to fiber formation. EP 0,188,091 discloses the production of a highly absorbent nonwoven web by coating the web with super-absorbent polymeric particles. U.S. Pat. No. 4,842,792 discloses fibers of improved cover, softness and wetting characteristics that are produced by caustic treatment of various polyesters which have continuous grooves in the cross-section. It is disclosed in the Journal of Applied Polymer Science, Vol. 25, PP1737-1744 (1980 ) that a fabric of increased dye uptake can be made using a concentrated non-ionic surfactant (TRITON X-100 made by Rohm and Haas Corp.) at a temperature between 180.degree. and 220.degree. C. for five minutes. Removal of excess liquid from fibers is disclosed in U.S. Pat. Nos. 3,458,890 and 3,786,574. Measurement of cohesion of crimped staple fiber is disclosed in U.S. Pat. No. 4,649,605.
All of these various aforementioned characteristics are important; however, unlike fabrics, staple fibers must also be satisfactorily processable in an economical manner under conventional production conditions by the equipment used in nonwoven and textile manufacture. Staple fibers are cut into suitable lengths (usually about 1 to 10 cm) for processing in a manner similar to natural staple fibers, such as cotton, in both textile and nonwoven machinery. These fibers must perform satisfactorily in such known operations as opening, blending, feeding, carding, bonding, heating, compressing, cooling, hydro-entangling, needle-punching, drawing, roving, spinning, knitting, weaving, and others as selected for the various nonwoven or textile materials.
Crimping of staple fiber by various means has been found to be an essential element in producing a certain controlled amount of fiber cohesion or resistance to pulling apart in forming carded webs. These webs of "opened" (separated) fibers are formed in flat-top or roller-top carding machines or the like as part of nonwoven or textile processes.
Poor crimp formation, especially in fibers with non-round cross-sections, has been associated with low and variable cohesion, weak webs, web separation, and poor processability during carding and/or subsequent operations. Relatively high lubricant levels (applied at room temperature), particularly above about 0.2 weight percent, of certain processing lubricants can cause unsatisfactory cohesion and processability problems in carding, etc. When such high levels of these lubricants are applied prior to the crimper (such as by conventional kiss rolls), low fiber-to-metal friction within the crimping chamber interferes with the capability to produce normal crimp frequency (crimps per inch) with sufficiently low (narrow) average crimp angle and relatively "V-shaped" crimp apex. Poor crimp is characterized by comparatively low and/or excessively variable crimp frequency and/or wide (open) average crimp angle; and/or comparatively "U-shaped" crimp apex.
Two types of commonly used processing lubricants are based on potassium lauryl phosphate or mineral oil with the addition of antistatic agents, friction modifiers, etc. as needed. At high levels (above 0.2 to 2 wt. % or greater) these and many other lubricants applied prior to the crimper using prior-art methods (usually lubricant-coated, rotating, contact rolls at approximately room temperature located remote from the crimper input) can have an adverse effect on crimp formation and/or tend to cause problems in carding by poor cohesion and/or by building up relatively quickly a detrimental coating on the carding wire and/or other problems. Additionally, these lubricants do not have good hydrophilic action.
Additionally, for certain applications, liquid-transport durability is a desirable characteristic but difficult to obtain in some man-made fibers. Certain man-made fibers, particularly those with suitable non-round cross-sections, have some initial liquid-transport characteristics. However, after wet usage, washing or scouring, the ability of these fibers to transport liquid can in some instances diminish significantly.
Any method of improving any of the aforementioned characteristics without significant adverse affects on other characteristics would be very desirable.